Long ago, even during the time when the Romans were first exploring the British Isles and establishing
their northernmost outposts, Stonehenge was already considered an ancient mystery.

Research and excavations have revealed that Stonehenge was built in phases, beginning perhaps as
early as 3,100 BC, and reaching a final form around 1,800 BC.
Its design seems to correspond to the observation of many astronomical events such as
solstices, eclipses, moon cycles, and more. Some theories of alignments are widely accepted.
Others are controversial because they could have developed by chance.

The most accepted astronomical correlation of the design is the axial alignment of the
monument with the summer and winter solstices.
There is clear evidence that at one time the famous Heel Stone had a partner,
and the sunrise on the summer solstice
was framed by the huge pair of standing stones when viewed from the center of the circle.
Six months later at the winter solstice the sunset was framed by one set of
the sarsenstone trilithons whose shape is the most familiar feature of the monument.

A complex 18.6 year cycle of the Moon may have also played a major role in the design.
Large "Station Stones" are aligned in the direction of the northernmost moonset and
the southernmost moonrise.

According the English Heritage Organization, the first stage of construction
was just a circle of heavy timbers surrounded by a ditch and an earthen bank.
Creating the ditch provided the material for the bank. The ditch would have been dug by hand using
animal bones. Deer antlers were used as pick-axes to loosen the underlying chalk and then the
shoulder blades of oxen or cattle were used as shovels to clear away boulders. Excavations of the
ditch have recovered antlers that were left behind deliberately and it was by radio carbon dating
that researchers concluded that the first henge was built over 5,000 years ago.

"That's where the mystery begins. We haven't just found old bones,
around the edge of the bank we also found 56 holes now known as Aubrey Holes, named after
the 17th century antiquarian, John Aubrey, who found them in about 1666. We know that these
holes were dug to hold wooden posts, just as holes were dug later to hold the stone pillars
that you see today. So this was the first stage built about 5,050 years ago, a wooden post circle
surrounded by a deep ditch and bank."english-heritage.org

Then around 2,500 BC (2,400 years before the Romans advanced into
Britain), it was rebuilt using stones. Bluestones were used first, which are the smaller
stones of the monument. Geologist have determined that these came from the Prescelli Mountains in Pembroke,
South Wales, 380kms (245 miles) away, perhaps dragged on rollers and sledges to the headwaters on
Milford Haven, and then loaded onto rafts. Placed on a raft, a large mass is relatively easy to transport.
The rafts could have travelled by water along the south coast of Wales
and up the rivers Avon and Frome, before being dragged overland again to near Warminster in
Wiltshire. The final stage of the journey was mainly by water, down the river Wylye to Salisbury,
then the Salisbury Avon to west Amesbury. The journey covers nearly 240 miles.
It was an amazing feat when you consider
that each stone weighs about five tons. It required unbelievable dedication by these people
with their ancient technology to
bring the stones all the way from South Wales. Such huge expenditures of man-hours in the ancient world
are thought to be usually associated with spiritual motivations.

Before the second phase of Stonehenge was complete, work stopped and there was a period of
abandonment. Then some later generations renovated, building a bigger and more complicated
monument. That construction phase lasted until about 4,300 years ago.
The remnant of that effort is the Stonehenge we know today.

The bluestones were dug up and rearranged and this time even bigger stones were brought in
from the Marlborough Downs, 25 miles away. These giant sandstones, or sarsenstones as they
are now called, were hammered to size and shaped using balls of stone known as mauls. Even today you can
see the drag marks. Each pair of stones was heaved upright and linked on the top by the lintels.
To get the lintels to stay in place, they made joints
in the stones, linking the lintels in a circular manner using a tongue and groove joint, and subsequently
the upright and lintel with a ball and socket joint, or mortise and tendon. This was all cleverly
designed on the alignment of the rising of the summer solstice sun and the setting of the winter
solstice sun.

How did they move the sarsenstones, some weighing more than 50 tons?
How did they get them to stand upright? Nobody really knows for sure. It required
sheer muscle power and hundreds of men with ropes to move each of these megaliths.
Modern calculations show that it would have taken 500 men using leather ropes to pull one stone,
and another 100 men to move and lay the huge rollers in front of the sledge.

These larger stones were arranged in an outer circle with a continuous run of lintels on top. Inside the circle,
the five huge famous trilithons were placed in a horseshoe arrangement. The open end
of the horseshoe faces towards the Heelstone
and the 1.8 mile long avenue that they built that leads to the river Avon.